Spectroscopic techniques are based on the absorption and emission of electromagnetic radiation.The most generally used spectroscopic techniques are: Ultraviolet-Visible (UV-V), Fluorescence and Phosphorescence, Infrared (IR), Raman, and Nuclear Magnetic Resonance (NMR).
In all these techniques emitted or absorbed radiation is defined by its wavelength and intensity. These magnitudes are related to the molecular structure of the specimens and to their concentration in the sample analyzed. For this reason, spectroscopic techniques are considered a powerful tool for microstructural characterisation of materials.
Two experimental techniques which are used to detect changes in vibration energy states are infrared spectroscopy (IR) and Raman spectroscopy. Although both spectroscopic methods are concerned with vibrations in molecules, they differ in the manner in which interaction with the exciting radiation occurs. IR spectroscopy is associated with changes in the bond dipole moment. Raman spectroscopy is concerned with changes in the polarisability of the bond when vibrations occur. For this reasons, complementary information is obtained between both techniques.